Streptococcus pneumoniae is still a major cause of morbidity and mortality around the world and its most common clonotypes are resistant to most first line antibiotics. Many of its most important virulence proteins constitute a family of cholie-binding proteins which are surface attached through their avid binding to the phosphocholine in the membrane lipoteichoic acids or cell wall teichoic acids. This project investigates the virulence and protection-eliciting properties of pneumococcal choline-binding protein A (PcpA). PcpA contains leucine-rich repeats (LRR). Other proteins belonging to the LRR super family have a variety of functions such as cell adhesion, signaling, RNA processing, and extra cellular matrix assembly. PspA in most strains is regulated through the relative concentrations of both zinc and manganese with the result that it is expressed in invasive disease in the lung, blood and organs; but is not expressed during colonization of the nasal mucosa. It is known that PcpA is a virulence factor in the lung and blood but not in nasal colonization. Immunity to PcpA can offer protection against pulmonary infections and sepsis; but not against colonization. My preliminary studies using A549 transformed lung epithelial cells demonstrate that PcpA can contribute to adherence of live pneumococci. My proposed research will investigate the possible role of PcpA as a contributor to in vitro adherence of pneumococci to primary human ciliated lung endothelial cells and to in vivo adherence of live pneumococci to lung cells during an infection. I will also examine PcpA's role in dissemination of pneumococci from the lung into the blood and organs. I will conduct parallel studies to evaluate the ability of immunity (including passive antibody) to PcpA to protect against adherence to host cells, and dissimilation into host tissues. Since it is likely that PcpA can bind host molecules, it may also modulate innate immunity. To monitor these potential effects we will collect data on cytokine responses from each of our in vivo and in vitro experiments, and will conduct separate histopathology studies to see if part of PcpA's virulence effects may involve modulation of innate immunity and inflammation.